sim: m32r: unify ELF & Linux traps logic

sim: m32r: unify ELF & Linux traps logic

This makes the simulator work the same regardless of the target (bare
metal m32r-elf or Linux m32r-linux-gnu) by unifying the traps code.
It was mostly already the same with the only difference being support
for trap #2 reserved for Linux syscalls.  We can move that logic to
runtime by checking the current environment operating mode instead.